The present invention relates to a trolley for the support of print cylinder assemblies as used in the stations of rotary printing machines.
Rotary machines used to implement both rotogravure and flexographic processes incorporate a number of print stations, each of which producing a single color. Each station comprises a revolving print cylinder bearing an image to be reproduced, against which a web of material is urged by an impression cylinder in such a way as to receive the image. The single station also comprises an arrangement for supplying ink to the cylinder, whether through a pumped system or by simple immersion, and a blade (the `doctor`), by which superfluous ink is wiped from the cylinder.
Each such assembly comprising print cylinder, ink supply system and doctor is provided further with accessories, such as devices designed for correct positioning and adjustment of the ink rail, doctor blade, ink vessels, etc...
In operation, the web is fed between the print and impression cylinders of each successive station, receiving one color component of the composite image at each station as it proceeds.
With each printing run completed, preparation for another (with a different image) clearlY involves changing over all print cylinders at the various stations.
Such a procedure is notably time-consuming, as the print cylinder must be lifted from its bearings and replaced by the cylinder needed for the next run; in addition, new inks must be put into the relative systems, all parts in contact with the ink having been thoroughly cleaned and flushed, whereupon the cylinder must be correctly positioned in relation to the station, and the doctor in relation to the cylinder. Needless to say, the changeover procedure must be carried through for each single station. Furthermore, the general problems thus outlined are aggravated further by the fact that print cylinders are typically heavy and cumbersome.
With changeover in progress, the machine clearly must remain at a standstill of duration dependent upon the number of individual stations; in effect, the interruption is never less than two or three hours, and given the high purchase price of rotary printing equipment, every stoppage represents an increase in overheads which, in practice, denies cost-effective operation in the case of small runs; at all events, down time will constitute a part of the costs in any contract undertaken, and persons skilled in the art know full well that where rotary printing equipment is involved, such costs run into hundreds of dollars per hour.
For some time now, the operation of changing over print cylinders has been speeded up by the use of trolleys. Each cylinder is carried by a relative trolley that can be positioned beneath the print equipment installed at each station, in such a way as to facilitate fitment and removal of cylinders generally, into and from corresponding stations. The standard practice is to utilize two trolleys per print station; thus, while one trolley remains with the machine, in readiness for removal of the cylinder, and if necessary, the ink supply, the spare trolley can be equipped with a new cylinder and ink supply in readiness to replace the trolley removed.
With the replacement trolley brought into the machine, it then remains to position the cylinder correctly in relation to the station and make the connection to the drive system by which it is set in rotation, and then effect all adjustments, e.g. to the ink supply system and the doctor, such as are required to ensure faultless printing.
Even with this method, the time needed to effect a changeover between jobs will never be less than two or three hours, especially where the machinery incorporates a significant number of stations. A further drawback encountered with this changeover method stems from the need to move spare trolleys around internally of the print room; even carrying a print cylinder alone, the type of trolley in question is notably heavy and difficult to handle. Accordingly, the object of the present invention is to overcome the drawbacks described above through the adoption of a trolley that ensures a drastic reduction in down time between production runs, and presents no great handling problems.